<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="https://unpkg.com/vue@3/dist/vue.global.js"></script>
    <style>
        div {
            font-size: 4em;
            color: skyblue;
            background-color: #ddd;
            width: 300px;
            height: 200px;
            border: 2px solid black;
            margin: 0 auto;
            padding: 0;
            text-align: center;
            border-radius: 20%;
        }
    </style>
</head>

<body>
    <div id="app">
        <p>{{date}}</p>
    </div>
    <script>
        Vue.createApp({
            data() {
                return {
                    date: '00:00:00'
                }
            },
            mounted() { 
                setInterval(() => {
                    let d = new Date();
                    let h = d.getHours() < 10 ? '0' + d.getHours() : d.getHours();
                    let m = d.getMinutes() < 10 ? '0' + d.getMinutes() : d.getMinutes();
                    let s = d.getSeconds() < 10 ? '0' + d.getSeconds() : d.getSeconds();
                    this.date = h + ':' + m + ':' + s;
       }, 1000);
            }
        }).mount('#app')
    </script>
</body>

</html>